TasksRepository.setVisibleTasks can add/remove listeners while HighResLoadingState.updateState iterates over them.
Bug: 408978565
Flag: com.android.launcher3.enable_refactor_task_thumbnail
Test: SwitchBackToSplitFromRecentGesturalNavLandscape#switchBackToSplitFromRecent
Test: Manual - made exception extremely likely by constantly adding/removing listeners. Could easily repro exceptions, then added this CL and could no longer repro.
Change-Id: Ic04717527fcbdb9301a6e313f9e666e2f5135b3e